Method of applying patterned metallization to block filter resonators

ABSTRACT

An embodiment of the present invention provides a method of applying patterned metallization to a ceramic block comprising applying a photodefinable ink to said ceramic block; drying said ink; exposing said photodefinable ink to UV radiation through a predefined mask according to the thickness of the film to form a pattern; developing said pattern in a developer solution thereby forming a patterned ceramic block; and rinsing, drying and firing said patterned ceramic block.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/736,467, filed Dec. 15, 2003, entitled, “METHOD OF APPLYING PATTERNEDMETALLIZATION TO BLOCK FILTER RESONATORS” to Chiu et al. which claimedpriority to US Provisional Patent Application Ser. No. 60/445,350,“METHOD OF APPLYING PATTERNED METALLIZATION TO BLOCK FILTER RESONATORS”filed Feb. 05, 2003, by Luna H. Chiu.

BACKGROUND OF THE INVENTION

The present invention generally relates to metallization, patterning ofelectrodes onto block type filters, diplexers and resonators. Thephoto-definition method is especially useful on small resonators havingany dimension less than 4 mm in size.

The concept of RF ceramic block type filters is well known in the art.Ceramic block filters are constructed of a high Q ceramic material andare typically coupled to other electronic circuitry through soldermounting pads, wires, cables and pins coupled to conductive connectionpoints on external surfaces of the blocks. These ceramics are also usedto construct duplexers and other electronic components. The productionof block filters starts with a ceramic resonator, typically a square orrectangular part having a length, width and height, and in most casesthis resonator will have a through hole in the center. The dimensions ofthe width and height are usually the same in a single resonator andthese two dimensions define the profile of the block. Once the ceramicblock is made, metallization (usually silver) is placed on all surfacesincluding the inside surface of the through hole. This is normallyperformed via a dip coating method. Typically, vendors of resonatorproducts will then sand or blast off the metallization on the topsurface only. Patterning of surfaces is usually not a provided service.

In prior art, a ceramic block is sintered and then blanket metallizationis usually placed using a dip coating method. Then the sides thatrequire metallization patterning are cleaned off or left uncoated. Thepatterning is traditionally performed by screen printing featuresdirectly on substrates followed by a firing step. However, in thepresent invention and devices of similar size, screen printing can notbe used due to the feature sizes and tolerances required. For example,the block part itself is a 3 mm×3 mm square and in some cases thecorners are rounded instead or square with a center through hole. Therequired spacing feature size was less than 4 mm with line sizes lessthan 10 mm. To ensure a good print with good edge definition andtolerances, this would be very expensive and nearly impossible. Also,due to the fact that the filter of the present invention is designed for1.8-2.3 GHz range, the tolerances required are much more stringent thanstandard screen printing usually allows.

Another method in prior art for applying a pattern to a block ceramicfilter is through a subtractive process such as chemical etching orlaser ablation to take off the excess metal in order to obtain a patternon the ceramic block. In the case of chemical etching of the metal, itis possible that the solutions used can adversely affect the ceramicmaterial surrounding the pattern. Also because this step would be donepost firing, the etching chemicals used are usually harsher than themethod defined in this invention. For this process it would be difficultto produce a pattern on a rounded corner block.

Therefore, a strong need in the industry exists for a novel method toapply to metal etching.

SUMMARY OF THE INVENTION

The present invention provides an electric communication signal blockresonator, comprising a block of dielectric materials having an outsidesurface including a top surface, a bottom surface, and at least firstand second side surfaces. The block defines at least one through-holeand each through-hole extends from an opening in the bottom surface toan opening in the top surface. Further, a metallization is deposited viaa photodefinable process onto said block. The metallization includesinput/output coupling metallization deposited via a photodefinableprocess as well as metallization of tunable varactors deposited via aphotodefinable process. The electric communication signal blockresonator can further include at least one additional block ofdielectric materials having an outside surface including a top surface,a bottom surface, and at least first and second side surfaces. The atleast one additional block defining at least one through-hole, eachthrough-hole extending from an opening in said bottom surface to anopening in said top surface and wherein a metallization is deposited viaa photodefinable process onto said at least one additional block; andsaid block of dielectric material and said at least one additional blockof dielectric material are connected via an iris between said block ofdielectric material and said at least one additional block of dielectricmaterial.

The present invention also provides for an RF filter. The RF filtercomprising a block of dielectric material; said block of dielectricmaterial having an electrode pattern that adheres to at least onesurface of said block; said electrode pattern consisting of aphotodefinable metallization covering at least one surface of said blockof dielectric material converted to a photodefined patternedmetallization on at least one surface of said dielectric material. Theaforementioned RF filter can also provide the electrode patternconsisting of a photodefinable metallization covering at least onesurface of said block of dielectric material converted to a photodefinedpatterned metallization on at least one surface of said dielectricmaterial. Further, the electrode pattern can consist of a photodefinablemetallization covering all surfaces of said block of dielectric materialconverted to a photodefined patterned metallization on from one to allsurfaces of said dielectric material. The metallization of the RF filtercan include input/output coupling metallization deposited via aphotodefinable process or can include metallization of tunable varactorsdeposited via a photodefinable process. The unique properties of thepresent invention provide that at least one of said photodefinedmetallic patterned surfaces are less than 4 mm square.

Also, the present invention provides a method of applying patternedmetallization to a ceramic block comprising the steps of: applying aphotodefinable ink to said ceramic block; drying said ink; exposing saidphotodefinable ink to UV radiation through a predefined mask accordingto the thickness of the film to form a pattern; developing said patternin a developer solution thereby forming a patterned ceramic block; andrinsing, drying and firing said patterned ceramic block. This method canprovide that said ceramic block is an electric communication signalblock resonator or wherein said pattern provides inter-cavity couplingbetween adjacent and non-adjacent cavities of said ceramic blocks andfinally wherein said pattern defines an electrode pattern to produce anRF input and output for said electric communication block resonator. Themethod can also provide that said ceramic block is a waveguide apertureand said pattern provides a coupling probe that can be either electricor magnetic. Further, the pattern can be a metallization patterns forsolder mounting pads on said ceramic blocks. The pattern of the presentmethod can provide for metallization in conjunction with tunability thusreducing the need for trimming of metal to obtain the correct frequency.

Because of the processes of the present method, it can be used onrounded or square sides and on sizes of less than 4 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a two-pole coaxial combline block filter;

FIG. 2 shows a tunable two-pole coaxial combline block filter;

FIG. 3 shows the response of the tunable coaxial combline filter with nobias;

FIG. 4 shows the response of the tunable coaxial combline filter underbias;

FIG. 5 shows a 3D mechanical block filter that is to be metallized usingthe photo-definition process;

FIG. 6 shows the mask patterns required (a)solder pades for the blocks,(b) mask pattern for coupling lines and varactors mounting pads, (c)aperture window for coupling between clocks (d) coupling lines for asingle resonator, (e)solder pads for a single resonator;

FIG. 7 shows the front face of a block resonator with no pattern and ametallized through hole;

FIG. 8 shows a solder pad on a block filter patterned via a photodefinedprocess;

FIG. 9 shows an aperture coupling window on a block filter patterned viaa photodefined process;

FIG. 10 shows the front face of a block resonator with coupling linesand SMT solder pads patterned via a photodefined process;

FIG. 11 shows the process flow of the photodefined process; and

FIG. 12 shows the process comparison benefits of the photodefinedprocess illustrates a layout of the multilayer filter of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

It is an object of the present invention to provide a new means toproduce a metal pattern on single or multiple faces of a ceramic blockbased filter. The ceramic block filter can be either a fixed filter ortunable block filters.

The present invention is related to the system and process of placingmetallization patterns on small electronically tunable filters made indielectric block form. The system and method of metallization of coursecan be performed on a fixed block filter as well. The tuning elementscan be voltage-controlled tunable dielectric capacitors placed on theceramic block. Alternatively, MEMS varactors or diode varactors can beused to make tunable filters, although with limited applications. Theactual metallization pattern given as an example in this invention isunique to the tunable filter using tunable dielectric capacitors;however, as mentioned above, the process described herein can be used inany type of block filter, tunable or fixed.

Patterning of surfaces on the block filter resonator is usually neededfor many designs. For example, on a block filter, well defined solderpads need to be separated from the rest of the resonator metallization.Other defined metallization patterns could include I/O pad generation,coupling lines, aperture windows and tuning lines.

The aforementioned difficulties are overcome in the present invention byproviding a novel method to apply to metal etching. In the laserablation method, it has been known that the directed energy of the lasercauses adverse Q effects during the lasing process. Subsequently, thematerial would require heat treatment. The size of features required forhigher frequency can be much smaller than the spot size of an ablatinglaser. Therefore this method of patterning may be limited as the blockfilters shrink down to below 2 mm in profile.

A third way to produce a pattern (however, this method is not normallyused in the block filter industry) is to use standard semiconductorphoto methods to pattern metal. However, this solution is usually moreexpensive and time consuming.

The present method is unique and a combination between a thick film andsemiconductor approach. The tunable block filter, which was made usingthis new process consists of a ceramic block with metallization in someareas to form a coaxial combline structure.

Turning now to the figures, FIG. 1 shows a front view of a two-polefilter 100 of the present invention. It consists of two coaxial comblineresonators 102 and 104 coupled to each other through an iris 120. Oneend of the resonators 102 and 104 is open and the other end is short.The access coupling to the resonators 102 and 104 is achieved by aprobe, which consists of a metallizing part of the dielectric at theopen end of the resonators, as shown in FIG. 1 at 106 and 108. All othersurfaces are metallized ground. The input/output coupling metallization105 and 110 has been extended to the perpendicular surface and isolatedas shown for SMD applications. Also depicted in FIG. 1 in the front vieware the metallized through holes in the ceramic blocks at 115 and 125.

Shown at 165 is the back view of the two pole filter 100 with a view ofresonators 105 and 110 shown from the back. Again, the input/outputcoupling metallization shown in this depiction as 105 and 110 has beenextended to the perpendicular surface and isolated as shown for SMDapplications. The metallized surface for ground can be seen in the backview as 140 and 160 for respective resonators. The back end ofmetallized through holes 115 and 125 can be seen in this back view aswell.

Filters with a higher number of poles can be made by simply adding moreresonators between the two resonators as shown in FIG. 2 at 200 withresonators 205 and 220 coupled by iris 240. Metallized through holes inthe ceramic are depicted at 235 and 245 and tunable varactors areintegrated with resonators at 230 and 250. Additional tunable varactorscan be added as well as shown at 225 and 255 with DC bias voltageprovided at 260. Again, input/output coupling metallization is depictedat 210 and 215 with areas of non-metallization used for isolation shownat 212 and 214.

The tunable block filter can be achieved in another form in which thereis no coupling iris 240 as in a coaxial combline structure as shown inFIG. 3 at 300. The resonators are still combline-coupled to one anotherto define a monoblock filter with resonator 330 and input/outputcoupling metallization at 310 and 315. Further, the metallized throughholes in the ceramic block are present at 320 and 325. The back view ofthe tunable block filter of FIG. 3 is shown generally at 335 withinput/out coupling metallization at 340 and 345 and metallized throughholes depicted at 350 and 355. Again, the back view of FIG. 3 providesdepection of the metallized surface for ground 360.

FIG. 4 shows an example of two-pole monoblock filter. To providetunability to this filter, one or two tunable varactors 415, 425, 445and 450 will be placed near the open end of the resonators 402 and 404.Filters with a higher number of poles will be made by simply adding moreresonators between the two shown in FIG. 4. Metallized through holes areprovided at 430 and 440. DC bias voltage that can be used for tunablevaractors is depicted at 435.

A 3D mechanical block filter that is to be metallized using thephoto-definition process of the present invention is shown in FIG. 5 at500. Based on this 3D design, one resonator (e.g., 505) would requiretwo sides to be patterned and for the other resonator three sides wouldrequire patterning (e.g., 525). As shown more clearly, metallizedthrough holes are shown at 530 and 510. The solder pads used forplacement of the optional varactors are depicted at 540, 545, 550 and555 and the RF ports shown at 535 and 560.

FIG. 6 a-6 e depict the images of the metallization masks required. Theshaded area is the indicator for where the metal is applied and the typeof metal pattern required. Specifically: 605 shows the mask patterns togenerate solder pads; 615 shows the clear area on the mask where it willbe metallized with metal for a RF I/O solder pad; 620 shows the cleararea on the mask where it will be metallized with metal for ground; 630shows the clear area on the mask where it will be metallized with metalfor the DC bias port; 610 shows the mask patterns to generate solderpads; 635 shows the clear area on the mask where it will be metallizedwith metal for DC bias port; 640 shows the clear area on the mask whereit will be metallized with metal for ground; 650 shows the clear area onthe mask where it will be metallized with metal for RF I/O solder padTurning now to FIG. 6 b, 655 shows the mask patterns for coupling linesand varactors mounting pads. In FIG. 6 c at 660 is shown the maskpattern to generate aperture window for coupling between clocks; 665shows the chrome area on the mask where it will be open aperture forcoupling; 670 shows the clear area on the mask where it will bemetallized with metal for ground. Now looking at FIG. 6 d, 675 shows themask pattern to generate coupling lines for a single resonator.

FIG. 6 e at 680 generally depicts a mask pattern to generate solder padsfor a single resonator. Specifically: 685 shows a clear area on the maskwhere it will be metallized with metal for DC bias port; 690 shows aclear area on the mask where it will be metallized with metal for DCbias port; and 695 shows a clear area on the mask where it will bemetallized with metal for ground.

In the present preferred embodiment in 6 a through 6 e the resonatorshave a profile of 4 mm×4 mm. Typically the resonators that are receivedfrom most manufacturers are 3.95 mm in profile with rounded corners.Thus, the camber of the corners caused the actual square area to beabout 9.0 mm². The center hole diameter of the preferred embodiment is0.9 mm although it is understood that diameter size is not crucial tothe present invention and alternative sizes can be utilized. Initially,the preferred embodiment of the present invention can have the resonatorbeing obtained with a metallized center through hole and all sidesmetallized except for the top face. In order to produce the requiredpatterns, one method would be to have the metallization sanded off fromtwo of the sides; however, this step would not be required forproduction. A basic process to achieve the patterns shown in (a)-(e)that can be used is described as example 1 illustrated below withreference to FIGS. 7, 8, 9 and 10.

FIGS. 7, 8, 9 and 10 show different views of the final metallized part.FIG. 7 shows the front face 710 of the block resonator 700 prior topatterning. The metallized throughhole is shown at 730.

FIG. 8 shows the bottom face 810 of the block 800 after patterning asolder pad 840. FIG. 9 depicts one side 910 of a block resonator 910after patterning with an aperture window 920 defined on the surface offace 910.

Finally, FIG. 10 at 1000 shows the front face 1020 after patterning1010, 1030, 1040 and 1060 which provide solder points for mountabledevices and coupling lines.

The process of patterning to provide the metallization of FIGS. 7, 8, 9and 10 will now be described in greater detail. Thus, the process usedto produce the metallization pattern is to photodefine a pattern usingphotodefinable metal. A typical process flow is shown in FIG. 11, forplacing a photodefinable pattern onto a block filter. Usingphoto-definition as the preferred method allows for the followingbenefits over the state of the art.

1) As compared to screen printing, the feature size and tolerancesachievable is much smaller and more accurate. In fact as frequencyincreases and filter sizes decrease, the area and metal pad size willneed to become smaller and more accurate.

2) As compared to typical semiconductor methods, the process is muchsimpler and there is no need for the expensive and time consuming vacuumdeposition methods. Also, for thin film or vacuum deposited methods suchas sputtering and e-beam, the thickness of the metal is limited by theefficiency of the process. Thicker (greater than 3 microns) metals arenot usually produced. As compared to an etchable metal process the totaltime and steps are less. For example, in the case of using an etchablethick film metal, the film would need to be applied by screen printingor dip-coating. The metal is then dried and fired. After this process,photoresist application is performed and exposure to UV through a maskas well as developing of the pattern would be required. Then removal ofthe metal would be performed with harsher acids such as potassium iodideor cyinide solutions. Then final removal of resist and cleaning (plasma,RIB) would take place. It is possible in the case of harsher chemicalsthat they may damage the ceramic surfaces in this case post annealingsteps may be required to bring the ceramic back to its originalproperties. Another issue could be getting the photoresist into thethrough-hole so that the metal is not taken away.

4) In the case of using laser trimming or laser ablation as the methodfor patterning of the metal, a limitation on the feature size would bethe spot size of the laser, usually the smallest sizes achievable isabout 50 microns. However, for complex designs on a surface laserpatterning is a relatively slow process. The time consumption depends onthe amount of power and complexity of the pattern. For higher powers thelasing process actually decreases the quality factor of the resonatorand a post annealing step is required to bring the material back to itsoriginal value.

In a first embodiment, an overview of the typical process for squareblock filter metallization patterning using a photodefinable processfollows the steps of FIG. 11 at 1100. Elaboration on each step followsbelow. At step 1110, a blanket coat of the surface of the dielectricusing a photo-definable metal paste is accomplished. Next, at step 1120,the ink between is dried using a hot plate or drying oven. Next, at step1130, part of the surface is exposed to UV through a predefined maskaccording to the thickness of the film. At step 1140, the pattern isdeveloped in the developer solution and then rinsed and dry the part instep 1150. Finally, in step 1160 the part s fired.

A typical set of processing conditions is shown below. These types ofparameters work for metallization of block filters that have squarecorners, however, filter blocks in most cases will have rounded edgeswhich require some process changes; these changes are considered in thenext example.

1) The first step is the application of a photosensitive metal ink. Aphotosensitive metal ink is an ink which contains metal particles inaddition to photosensitive organic compounds. The application of the inkin present application in a preferred embodiment is performed by blanketcoating of the metal, a typical way is screen printing.

2) This ink is then dried either in a furnace or hot plate. The dryingtemperature is between 70C-100c. The drying time is between 5 to 30 min.

3) After the ink is dried, the part is then exposed to UV through amask; the mask can be positive or negative depending on the nature ofthe ink. The exposure time is between 40-80 sec depending on the filmthickness. The developer time also varies with the developmentmethods—immersion developing, spray developing, puddle developing. In afirst embodiment of the present invention was used immersion developingand develop time is around 60 sec.

4) The pattern is now present on the block and ready for firing. Atypical firing profile is 30 minutes to 850° C. holding for 10 mins andthen cooling the furnace down. The total firing time is about 1.5-2.0hours.

The final metallization film thickness of this embodiment was measuredfrom the present block filter at about 5 μm. However 8-10 microns iseasily achievable.

In the following second preferred embodiment of the present invention,an overview of the typical process for photodefinable metallization isdescribed, which modifies the process described above to allow for arounded corner blocks.

1) In the screen printing process of this second preferred embodimentwas used a finer mesh and thinner emulsion screen. This type of screenprovides a more even print and better uniformity around the edges of aresonator. Also, softer squares were used as well as more down stop foruniformity reasons.

2) Drying time was increased to ensure that the ink was uniformly dry.The temperature used was on the higher side of the range at about 95° C.

3) Proximity exposure is used as opposed to contact exposure.

4) 2.5 mol % solution of Sodium Carbonate is used instead of a 0.8-1.0%normally used for flat substrates.

Turning now to FIG. 12 there is shown at 1200 a synopsis of theprocessing steps required. Process steps 1210 show the step that isbeing accomplished and whether each of the following is required:photodefined 1220; screen printed 1230; etched 1240; semiconductorpatterning 1250; or laser patterning 1260. The chart shows that thetotal number of steps is less for the photodefinable process. Further,it may not be apparent, but the time required on some of the steps isconsiderably less than in the other processes. For example, the laserablation process is a single step but can be time consuming per part.Another example is the vacuum metal deposition which requires time aswell. Thus, time required for the process of the present invention is animportant benefit.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample, and not limitation. It will be apparent to persons skilled inthe relevant art that various changes in form and detail can be madetherein without departing from the spirit and scope of the invention.

The present invention has been described above with the aid offunctional building blocks illustrating the performance of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed. Any such alternate boundaries are thus within the scope andspirit of the claimed invention. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

All cited patent documents and publications in the above description areincorporated herein by reference.

1. A method of applying patterned metallization to a ceramic blockcomprising: applying a photodefinable ink to said ceramic block; dryingsaid ink; exposing said photodefinable ink to UV radiation through apredefined mask according to the thickness of the film to form apattern; developing said pattern in a developer solution thereby forminga patterned ceramic block; and rinsing, drying and firing said patternedceramic block.
 2. The method of claim 1, wherein said ceramic block isan electric communication signal block resonator.
 3. The method of claim1, wherein said pattern provides inter-cavity coupling between adjacentand non-adjacent cavities of said ceramic blocks.
 4. The method of claim2, wherein said pattern defines an electrode pattern to produce an RFinput and output for said electric communication block resonator.
 5. Themethod of claim 1, wherein said ceramic block is a waveguide apertureand said pattern provides a coupling probe that can be either electricor magnetic.
 6. The method of claim 1, wherein said pattern is ametallization pattern for solder mounting pads on said ceramic blocks.7. The method of claim 1, wherein said pattern provides formetallization in conjunction with tunability that reduces the need fortrimming of metal to obtain the correct frequency
 8. A method forproduction of photodefinable metallization on electric communicationsignal block resonators with rounded edges and square edges, comprising:applying a photodefinable ink to said block; drying said ink; exposingsaid photodefinable ink to UV radiation through a predefined maskaccording to the thickness of the film to form a pattern; developingsaid pattern in a developer solution thereby forming a patterned block;and rinsing, drying and firing said patterned block.
 9. The method ofclaim 8, wherein said metallization includes input/output coupling. 10.The method of claim 8, wherein said metallization includes metallizationof tunable varactors.
 11. The method of claim 8, wherein saidmetallization includes metallization of metallized through holes.